Typically, a front part of the passenger compartment of an automobile is reinforced by a cross member structure consisting of a box-like structure defined by a dashboard panel and a cowl panel having required rigidity and mechanical strength. Since a complex air duct structure is necessary in the vicinity of the dashboard of an automobile, for instance, for ram pressure ventilation or, in other words, for introducing fresh air from outside by the wind pressure produced by the motion of the automobile, defrosting or demisting the windshield by blowing warm air thereonto by a motor-driven fan, and circulating warmed or cooled air in the passenger compartment, the interference between the cross member structure provided in the forward end of the passenger compartment for reinforcement with such an air duct structure could be a problem in designing the automobile body.
It is known to define an air duct in the interior of the cross member and utilize a part of the cross member as an air duct structure for guiding air to an air conditioner or a blower for air conditioning the passenger compartment or for removing moisture from a windshield, as the case may be, but, in such a case, since a number of holes must be provided in the structure to the end of introducing fresh air into the air duct structure, diverting air to various air outlets in the passenger compartment for air conditioning and letting out air uniformly therefrom for defrosting or demisting the windshield, it will be difficult to give a desired reinforcement capability to the cross member. Particularly since the cross member is located very close to the driver, any vibration of the cross member due to lack of rigidity of the cross member, no matter whether it is caused by the air flow in the air duct structure or transmitted from the engine or other moving parts of the automobile, can severely impair the driving comfort of the automobile.
Also, depending on weather conditions, for instance when it is humid or raining, it is preferable to have both ventilation by ram pressure and defrosting action by a blower at the same time. In an air duct structure which allows introduction of fresh air for ventilation and defrosting at the same time, much air is sucked by the blower and the flow rate of the fresh air for ram pressure ventilation tends to be insufficient. It is conceivable to provide an air duct for introducing fresh air by ram pressure and another air duct for introducing fresh air to be blown onto the windshield by a blower separately from each other, but such an air duct structure necessarily tends to be complex and makes manufacturing thereof both costly and difficult. And this problem will be even more compounded by the necessity to assure sufficient reinforcement capability to the cross member.